Our goal is to define mitochondrial iron metabolism in eukaryotes at the molecular and biochemical level by studying yeast genes that are involved in mitochondrial iron transport and utilization. YFH1 is the yeast homologue of the mammalian Frataxin gene, which is responsible for Friedreich Ataxia. Defects in YFH1 result in excessive mitochondrial iron accumulation due to a defect in mitochondrial iron export and leads to respiratory deficit due to the generation of toxic oxygen radicals. We propose to determine how YFH1 affects mitochondrial iron export. We plan to test the hypothesis that defects in mitochondrial iron export result from defects in the mitochondrial iron-sulfur cluster synthetic pathway, and that Yfh1p is involved in iron-sulfur cluster syntheses. Genetic experiments are designed to identify proteins that interact with Yfh1p by generating dominant negative alleles of YFH1. Using biochemical assays to measure iron-sulfur cluster synthesis in isolated mitochondria, we plan to examine the affect of YFH1 mutant alleles. We also propose genetic approaches to identify genes that regulate the mitochondrial iron cycle. Different genes are implicated in mitochondrial metal transporter. We propose genetic and biochemical approaches to test the hypothesis that these genes are transition metal transporters which provide iron and other transition metals for mitochondrial processes. The genetic approaches involve identifying the phenotype of cells with deletions in multiple transporter genes. The biochemical approaches include studying metal transport in isolated mitochondria and in liposomes reconstituted with specific transporters. In mammals defective heme biosynthesis results in mitochondrial iron accumulation in reticulocytes but not in other cell types. We discovered that in yeast, defective heme synthesis inhibits high affinity iron transport, which prevents mitochondrial iron accumulation. We propose to determine the mechanism by which the absence of heme affects iron transport.